(1) Field of the Invention
The invention relates to an apparatus for displaying a series of stationary images such that they form an animated display when seen by an observer in a moving vehicle in dark places, such as tunnels.
(2) Description of Prior Art
The placement of briefly illuminated, individual images along the route of a subway or other vehicle travelling in a dark place for the purposes of displaying an animated image has been presented in numerous patents including U.S. Pat. Nos. 917,587, 978,854, 3,694,062, 3,704,064, 3,951,529, 4,179,198, and 4,383,742. A variety of light triggering methods and display arrangements are presented in these patents. All the patents discussed below use an image display panel to present the image. The image display panels are mounted on the wall of a darkened place and located in close proximity to the route of a moving vehicle.
U.S. Pat. No. 978,854 (Czerniewski) uses a purely mechanical means of triggering the illumination of the image. A "shoe" attached to the moving vehicle lifts a shutter attached to the subway wall beside the train. A mechanism then permits light to momentarily illuminate the image within the image display panel mounted on the subway wall.
U.S. Pat. Nos. 917,587 (Good) and 4,179,198 (Brachet) use an electro-mechanical means of triggering the illumination of each image. These employ a mechanical device attached to the train which periodically closes an electrical circuit, triggering the illumination of the image within the image display panel.
U S. Pat. Nos. 3,951,529 (Gandia) and 4,383,742 (Brachet) use a determination of the vehicle's speed to trigger image illumination. The former assumes that the train travels at a predetermined speed each time it passes a section of track while the latter measures the train's speed by a radar type speed detector. Many image display panels are triggered to illuminate their images simultaneously.
U.S. Pat. Nos. 3,694,062 (Koenig) and 3,704,064 (Sollogoub) use the light from within the vehicle to trigger image illumination. A light detector associated with each image display panel monitors the light intensity coming from the passing vehicle. When the light shining on the image display panel is of great enough intensity the image is briefly illuminated.
U.S. Pat. No. 978,854 (Czerniewski), previously referred to, uses a stationary miniature image mounted within the image display panel. Light is shone through the miniature image and is magnified through various lenses and directed onto the back of a semi-transparent projection screen by a series of reflectors. The light source is attached to the moving vehicle. All the other patents mentioned above use a large size, back or front lit, image mounted as part of the image display panel.
A major problem with the designs put forward in previous patents is that they do not precisely and reliably trigger image illumination. In order that the observer can clearly see the image, each successive image must be illuminated at exactly the same position relative to the observer. If this process is not precise, the integration of the images will seem blurred. Using light from within the vehicle to trigger image illumination relies on the light reaching the panel-mounted image illumination sensor/trigger being of the same intensity for each image passed. This in turn relies on coordinated and precise panel to panel calibration of all image illumination sensor/triggers so that the light intensity which causes one image illumination to occur will cause image illumination in all image display panels. This method assumes that the calibration can be done economically and that the people observing the animated display do not block the light and thus cause image illumination to occur at different locations from one image display panel to the next. In addition the image will be lit at erroneous times by any light source above the image trigger illumination light threshold. This will include the light coming from the vehicle driver/operator's window. The operator of the vehicle will be distracted by the flashing images causing an unsafe situation.
Triggering methods which employ a determination of the vehicle's speed suffer from illumination accuracy problems as well. It would be very difficult and expensive to measure the speed of the vehicle with enough accuracy to coordinate image illumination and vehicle motion so that a satisfactory display was achieved. For example, a velocity measurement repeatability accuracy of + or -0.014% would be needed to reduce image illuminate location errors to + or -2.0 mm when the vehicle is travelling at 50 km/hr. The high level of accuracy is required to ensure that the image presented is not blurry. Apart from the problem of illumination accuracy this type of animation device suffers from the problem that it illuminates a large number of images at the same time without regard for the position of the observer relative to the image. In many cases the image will be partially obscured from view by window dividers making the presentation unclear and difficult to see.
The mechanical illumination triggering devices, referenced above, have inherent mechanical wear problems because of the high triggering rates and thus are not practical.
Periodically the operator of the animation system will change the images displayed. The large number of images (as many as 1,440 images per minute of display to give the film industry standard 24 frames per second at 50 km/hr) make the preparation and changing of the display images a potentially time consuming and expensive task. Time and expense can be reduced if a miniature transparent image (such as a photographic slide) is used in conjunction with a projection display system mounted inside each panel. Production of a series of miniature images could be accommodated at a low cost by adapting existing video tape or film to the required miniature image size. The size of the miniature image could be chosen so that standard photographic image transfer equipment could be used. The installation time required for the placement of a miniature transparent image inside an image display panel is much shorter than the time required for the installation of a large image of the fully projected size. Thus, using an image display panel equipped with a projected miniature transparent image will reduce ongoing production and maintenance costs. There are, therefore, significant advantages to the use of a projected miniature transparent image.
One of the above mentioned patents incorporates a miniature image and projection system into the image display panel. The major problem with the above mentioned patent is that it requires the light source to be mounted on the moving vehicle. Because the vehicle moves up and down and rocks back and forth the illumination source will not align correctly with the miniature transparent image causing distortion and poor viewing quality. In addition, the optical arrangement outlined in the previously mentioned patent requires much too large an image display panel for the installation to be practical or economical.